RFR: 8338668: Test javax/swing/JFileChooser/8080628/bug8080628.java doesn't test for GTK L&F

[Abhishek Kumar]

This test should have failed with the [changeset](https://github.com/openjdk/jdk/pull/20612) proposed for [JDK-4795384](https://bugs.openjdk.org/browse/JDK-4795384) but it didn't because GTK look and feel isn't supported in headless environment.

Fix is to run the test with headful environment on linux platform. 

Tested in CI pipeline and link attached to JBS.

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Commit messages:
 - added headful tag for linux platform

Changes: https://git.openjdk.org/jdk/pull/20671/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20671&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338668
  Stats: 14 lines in 1 file changed: 12 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20671.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20671/head:pull/20671

PR: https://git.openjdk.org/jdk/pull/20671